塑性混凝土特征指标尺寸效应的试验研究

Plastic concrete is widely used in cut-off walls of hydraulic structures. As shown in preliminary study, the compressive behavior of plastic concert shows size effect. But at present, the systematic research results are very few. To study the size effect on peak compressive strength， peak strain and residual stress of plastic concrete, experiments and analytical analysis are used in this project. Cylinder and prism specimens with same mix proportion, different bottom dimension and three different slender ratios are tested in uniaxial unconfined compression. Based on the data of strain and stress measured in the test, modifications and improvements can be made to the constitutive law proposed in the earlier work for plastic concrete in compression. Further analysis on experimental data are made to obtain characteristic indicators for plastic concrete in compression. Meanwhile, failure surfaces of plastic concrete are observed in meso-scale and micro-scale with the help of scanning electronic microscope. Based on this experiment, a proper theory can be chosen to study size effect of plastic concrete, and statistics of compressive strength and strain at peak stress can be obtained, thereby the failure mechanism and size effect of plastic concrete in compression being revealed. The change law of compressive strength and strain at peak stress for large-scale structures is derived analytically. The test method is reversed under normal condition in the lab. Therefore, reliable basis can be provided to determine the characteristics indicator for plastic concrete in compression, and to improve the design theory and method.

前期研究成果表明，广泛应用于水工建筑物防渗墙中的塑性混凝土存在尺寸效应现象，但目前对其系统研究成果甚少。本项目拟采用试验方法并通过理论分析技术，重点开展单轴无侧限抗压试验，通过采集、分析试件应力应变曲线，修正完善前期研究成果中塑性混凝土本构模型；采用数据挖掘技术获取反映塑性混凝土受压特性指标，研究塑性混凝土相同配合比、不同底面尺寸、3个高径比的圆柱体和棱柱体试件峰值抗压强度、峰值应力及残余应力的尺寸效应。利用扫描电镜观测塑性混凝土破坏面的细观特征，提供尺寸效应理论选择依据，统计归纳峰值抗压强度和峰值应变试验成果，揭示塑性混凝土受压尺寸效应规律及破坏机理，理论推导工程中大尺寸构件抗压强度和峰值应变的变化规律，结合现有实验室常规条件反演测试方法，以期为准确测定塑性混凝土受压性能力学指标提供科学依据，并为完善塑性混凝土受压构件设计理论及方法提供基础。

前期研究成果表明，广泛应用于水工建筑物防渗加固中的塑性混凝土存在尺寸效应现象，但单轴无侧限压缩试验试件最终破坏时，未出现粗骨料破碎现象，带来与普通混凝土尺寸效应的差异，且目前对其系统研究成果较少。本项目采用室内试验、理论分析及数值拟合方法，考虑配合比、高径比、试件形状和尺寸变化等因素，采用研制的试件成型和承载装置，对塑性混凝土受压性能特征指标尺寸效应开展研究。研究了机制砂掺率对塑性混凝土拌合物工作性能、抗压强度、峰值应变及应力应变曲线等的影响，并就机制砂替代河砂的可行性给出结论性建议；通过不同试验条件下的单轴无侧限压缩试验，总结提炼了棱柱体和圆柱体共性和特性破坏现象，得到了配合比和高径比变化只影响峰值应力、峰值应变尺寸效应幅值，且棱柱体峰值应力约为圆柱体峰值应力的1.1~1.2倍，但弹性模量无明显尺寸效应，同时，棱柱体弹性模量高于圆柱体弹性模量；引入尺寸效应系数反映峰值应力和峰值应变尺寸效应变化，采用基于能量释放的Bazant尺寸效应律和Carpinter多重分形尺寸效应律，分别建立峰值应力尺寸效应计算公式，在试验尺寸范围内二者具有较好的一致性和适应性，由此得到了临界尺寸和临界应力；提出了反映尺寸、配合比和高径比变化的峰值应变尺寸效应计算公式，并证明了其适用性良好；研究成果为准确测定塑性混凝土受压性能力学指标提供科学依据，并为完善塑性混凝土受压构件设计理论及方法提供研究基础，具有重要的科学意义。